Rcd tripping on no trip Eli test

[hoover]

Hi using a megger 1552 to do a few earth loops in a house. It's on the no trip function but still the rcd trips. Never had this before as usually the rcd holds out long enough to get the required reading for the earth loop imp. It's a tt system and the rcd ( 30 ma) is relatively new. Any thoughts?

 

[ezzzekiel]

have you tried the rcd tested alone without any circuits switched on, seen n/e faults cause rcds not trip and also a poor main earth (still never worked out why)

test rcd alone if same try a different one if it works start checking circuits

 

[tony mc]

What is the Ra ?

Forget that miss read the question!!

 

[netblindpaul]

Ramp test?
Any RCD test MUST be at the output of the RCD with ALL loads disconnected, are you following this procedure?

 

[telectrix]

i would first do a ramp test on the RCD. you may have leakage just below the threshold, and your loop test is taking it over.

 

[ezzzekiel]

Ramp test?
Any RCD test MUST be at the output of the RCD with ALL loads disconnected, are you following this procedure?

Which is a good point as most training (centres colleges books videos etc) tend to show meter being plugged into socket

 

[GLENNSPARK]

I dont think a low current loop guarantees that it wont throw the RCD when testing...my MFT will do just about every test you would need for installs ....but it wont do a low current Zs....I just wire out the RCD or just do the simple maths : Zs = Ze+ R1 R2..........

 

[sparkinlee]

Hi using a megger 1552 to do a few earth loops in a house. It's on the no trip function but still the rcd trips. Never had this before as usually the rcd holds out long enough to get the required reading for the earth loop imp. It's a tt system and the rcd ( 30 ma) is relatively new. Any thoughts?

When this happens to me it's usually because I've done something daft like get the test leads mixed up so I've got E & N reversed or something!

 

[platty1005]

just had a similar problem with a metrel. using the tester with 2 leads just Line and CPC it tripped the RCD using it as a 3 wire tester Line neutral and CPC it tested OK

 

[Deleted member 26818]

What model Metrel?
I thought the Zs test with Metrels had to always be done with 3 leads?
Don't you have to join the E&N leads together?

 

[MarkieSparkie]

Hi Hoover, the Megger 1552 MFT Hi current loop test is 2 wire, but No-trip loop test is 3 wire, this often traps the unwary. Trying to 2 wire, No-trip test with the 1552 WILL TRIP out the RCD, due to unbalanced current injection/loading.

 

[GLENNSPARK]

Hi Hoover, the Megger 1552 MFT Hi current loop test is 2 wire, but No-trip loop test is 3 wire, this often traps the unwary. Trying to 2 wire, No-trip test with the 1552 WILL TRIP out the RCD, due to unbalanced current injection/loading.

When i read that post i thought he was getting mixed up with doing a PFC Markie....

 

[hoover]

Hi Hoover, the Megger 1552 MFT Hi current loop test is 2 wire, but No-trip loop test is 3 wire, this often traps the unwary. Trying to 2 wire, No-trip test with the 1552 WILL TRIP out the RCD, due to unbalanced current injection/loading.

Hi. I'm using the plug lead in the socket outlet to do my Eli so would imagine it's the three lead method ok.

 

[hoover]

It's not an rcd test I'm doing mate, just an earth loop impedance.

 

[platty1005]

Hi Spinlondon Metrel easitest with a A1176 2 wire tip commander use this for Zs and the RCD trips use standard 3 wire lead connected to L N and E and it tests OK. The tip commander is quick and easy for most tests except Zs with an RCD check out the metrel catalogue item A1176 Tip commander

METREL TECHNICAL CATALOG 2011

 

[netblindpaul]

OK, my comment was wrt ELI, check the RCD on ramp to check it is not faulty.
The RCD test comment was a general one.

 

[SPARTYKUS]

i would first do a ramp test on the RCD. you may have leakage just below the threshold, and your loop test is taking it over.

My money's on Tel's answer.

 

[netblindpaul]

My money's on Tel's answer.

Quite, an earth leakage clamping would be a good test too.